gistfile1.scala

LiftRules.dispatch.append {
  case r@Req("some" :: "path" :: Nil,"",GetRequest) => {
    val accept = in.headers("accept")
    (accept.find(_.toLowerCase.indexOf("text/xml") >= 0).isDefined || 
      ((in.path.suffix equalsIgnoreCase "xml") && (accept.isEmpty || 
         accept.find(_.toLowerCase.indexOf("*/*") >= 0).isDefined))) 
    ? Full(XmlResponse(...))  | Full(JsonReponse(...))
  }
}